Papers by Keyword: Layered Structures

Abstract: High specific strength of Ti-based alloys and composites makes them highly requested materials in various structural applications, especially when lightweight is desired in high-strength constructions. When these alloys are used in layered structures, far advanced set of characteristics that combine different mechanical properties often non-compatible in a single layer uniform structure can be attained; for instance, high hardness or moduli systems are usually lacking of sufficient toughness. Mechanical properties of individual layer in multilayered materials can be controlled by changing chemical composition and microstructure within each layer specifically. In present study layered materials were formed by combination of the layer of Ti-6Al-4V alloy and metal matrix composites on its base reinforced with fine TiB and TiC particles. Structures were fabricated using blended elemental powder metallurgy (BEPM). The effect of different post-sintering thermo-mechanical treatments on structure of layered BEPM materials was studied. Processing parameters were assessed in terms of their influence on materials’ porosity, grain size and structure, distribution of reinforcement particles and layers integration. The effect of above mentioned structural characteristics on hardness of layered materials was evaluated.

Abstract: In this paper the authors present some of the results of research on the behavior of high entropy alloys used in ballistic protection structures. Bullet impact testing methodology and results on layered Ballistic Packages that incorporate high entropy alloys (HEA) are presented. The paper details the technological processes used to improve the mechanical characteristics of Ballistic Packages. The optimization of the high entropy alloy based layered ballistic composite structures is also investigated. Testing methodology of ballistic boxes, the special heat treatment processes, the homogenization and the artificial aging of high entropy alloys, designed and applied during scientific research; represent the novelties of the article. Ballistic Packages are layered structures which include combinations of the following materials: HEA, armored steel, ceramic plates and laminated polyamide fibers arranged in a predetermined order depending on the constructive version. Ballistic Boxes behavior was investigated by ballistic experimental methods and numerical simulation methods. For the numerical simulation a FEM with an explicit numerical code was used. The numerical and test results are consistent in underling the ballistic protection effectiveness of the investigated configuration.

Abstract: This paper explicitly highlights the failure analysis and study of thin walled composite beams (multi-cell and multi-tapered) in cantilever configurations when subjected to constrained torsional load, using MSC Patran / Nastran finite element package. Initially, the verification of the model was done with the analytical results in order to ensure the model accuracy. All the multi-tapered beams under examination are composed of closed section and three cell configuration with twisting moment applied at the free end. There is a vivid description of all the effects of different composite material and various stacking sequences on the margin of safety and failure loads. This paper also verifies the influence of various geometrical configurations (Beam lengths, tapered angles and point of variation of tapered angles) of beams on the failure loads. This paper would help in the wing design phase of modern agile and high speed aircraft in which multi-cell closed cross section beams are integral part.

Abstract: Shape memory alloys have a peculiar property to return to a previously defined shape or dimension when they are subjected to variation of temperature. Shape memory effect is facilitated by martensitic transformation governed by changes in the crystalline structure of the material. Martensitic transformations are first order lattice-distorting phase transformations and occur with the cooperative movement of atoms by means of lattice invariant shears in the materials on cooling from high temperature parent phase region. The material cycles between the deformed and original shapes on cooling and heating in reversible shape memory effect. Thermal induced martensite occurs as twinned martensite, and the twinned martensite structures turn into detwinned structures by deforming the material in the martensitic condition. Deformation of shape memory alloys in martensitic state proceeds through a martensite variant reorientation. The deformed material recovers the original shape on first heating over the austenite finish temperature in reversible and irreversible shape memory cases. Meanwhile, the parent phase structure returns to the twinned structure in irreversible shape memory effect on cooling below to martensite finish temperature and to the detwinned structure in reversible shape memory effect. Therefore, the twinning and detwinning processes have great importance in the shape memory behaviour of the materials. Copper based alloys exhibit this property in metastable β-phase region, which has bcc-based structures at high temperature parent phase field, and these structures martensitically turn into layered complex structures with lattice twinning following two ordered reactions on cooling.

Abstract: Shape memory effect is a peculiar property exhibited by certain alloy systems, and shape memory alloys are recognized to be smart materials. These alloys have important ability to recover the original shape of material after deformation, and they are used as shape memory elements in devices due to this property. The shape memory effect is facilitated by a displacive transformation known as martensitic transformation. Shape memory effect refers to the shape recovery of materials resulting from martensite to austenite transformation when heated above reverse transformation temperature after deforming in the martensitic phase. These alloys also cycle between two certain shapes with changing temperature.Martensitic transformations occur with cooperative movement of atoms by means of lattice invariant shears on a {110} - type plane of austenite matrix which is basal plane of martensite.Copper based alloys exhibit this property in metastable β-phase field. High temperature β-phase bcc-structures martensiticaly undergo the non-conventional structures following two ordered reactions on cooling, and structural changes in nanoscale level govern this transition cooling. Atomic movements are also confined to interatomic lengths due to the diffusionless character of martensitic transformation.

Abstract: Shape memory effect is a peculiar property exhibited by certain alloy system. This behavior is facilitated by martensitic transformation, and shape memory properties are intimately related to the microstructures of alloys; in particular, the morphology and orientation relationship between the various martensite variants. Martensitic transformation occurs in thermal manner, on cooling the materials from high temperature parent phase region. Thermal induced martensite called self-accommodated martensite or multivariant martensite occurs as multivariant martensite in self-accommodating manner and consists of lattice twins. Shape memory alloys are deformed in low temperature martensitic phase condition, and deformation proceeds through a martensite variant reorientation. Copper based alloys exhibit this property in metastable β - phase region.

Abstract: In this paper, addition of Fe-Ni, MnZn-ferrite, and CNF (carbon nanofiber) absorbers in the Kevlar fiber fabric-reinforced epoxy resin composites resulted in excellent absorbing properties as well as other required properties such as light-weight (as low as 2.2 g/cm³), small thickness (~2 mm), high mechanical strength (up to 380 MPa) and thermal stability (up to 120 °C). Reflection loss testing of the laminates FM-3 showed that the peak reflection loss was-45 dB at the frequency of 10.4 GHz, and the absorbing waveband at-10dB was 12 GHz (from 6 to 18GHz). The study also indicated that the content of the added absorbers was limited by the viscosity (or flowability) of the resin-absorber mixed suspensions.

Abstract: Martensitic transformations are first order solid state phase transitions and occur in the materials on cooling from high temperature. Shape memory effect is an unusual property exhibited by certain alloy systems, and based on martensitic transformation. The shape memory property is characterized by the recoverability of previously defined shape or dimension when they are subjected to variation of temperature. The shape memory effect is facilitated by martensitic transformation, and shape memory properties are intimately related to the microstructures of the materials. Martensitic transformations occur as martensite variant with the cooperative movement of atoms on {110}_β - type plane of austenite matrix. Martensitic transformations have diffusionless character, and the atomic movement is confined to interatomic lengths in the materials. The basic factors which govern the martensitic transformation are Bain distortion and homogeneous shears. Copper based alloys exhibit this property in metastable β-phase field.